The present invention relates to a golf club head having a hollow structure. More specifically, the present invention relates to a golf club head having a position of a head center of gravity projected on a face surface set in the vicinity of a face center by improving a head shape.
Conventionally, in many cases, a hollow golf club head used for a wood golf club has had a shape asymmetrical in an upper-lower direction and inverted-trapezoidal when seen from a front side. In the golf club head of such a shape, a head center of gravity is inevitably set high when a head thickness excluding a face portion is made uniform. Thus, by disposing a weight in a sole side of a head body or setting a thickness of a sole portion to be relatively larger, the head center of gravity is lowered such that a position of the head center of gravity projected on a face surface can be set in the vicinity of a face center.
However, there is naturally a limit on total weight of the golf club head. Accordingly, when a weight adjustment is made in order to correct unevenness of mass caused by the above-described head shape, it becomes difficult to add another weight in a backside of the head body in order to increase a depth of the center of gravity. Consequently, there has been a difficulty of making adjustments for a height of the center of gravity and for a depth of the center of gravity at the same time.
In addition, in the conventional golf club head, when a head volume is set large in order to improve stability of a hit ball, an adjustment of a head thickness and an addition of a weight are limited because of the limit on the total weight. Consequently, the unevenness of mass due to the head shape may not be sufficiently corrected, thus causing such a problem that the head center of gravity projected on the face surface can not be set in the vicinity of the face center.
An object of the present invention is to provide a golf club head capable of setting a head center of gravity projected on a face surface in the vicinity of a face center even when a head thickness excluding a face portion is made uniform, or a head volume is increased to a maximum.
In order to achieve the foregoing object, a golf club head in accordance with the present invention includes: a head body provided with a neck portion for fixing a club shaft in a heel side of a crown portion thereof. In this case, in a state of a face surface of the head body being set as a front, when a geometric face center of the face surface is set as an origin 0; a straight line extended in a right-left toe-heel direction in contact with the face center is set as an X axis; a straight line extended in an upper-lower crown-sole direction in an orthogonal relation to the X axis in contact with the face center is set as a Y axis; and a straight line extended in a forward-backward direction in an orthogonal relation to the X and Y axes is set as a Z axis, an absolute value of a sum of a Y coordinate value (YC) of a most bulged position C in a crown side of the head body and a Y coordinate value (YS) of a most bulged position S in a sole side of the head body is set equal to 2 mm or lower, an absolute value of a difference between a Z coordinate value (ZC) of the most bulged position C in the crown side of the head body and a Z coordinate value (ZS) of the most bulged position S in the sole side of the head body is set equal to 2 mm or lower, and absolute values of a Y coordinate value (YT) of a most bulged position T in a toe side of the head body, a Y coordinate value (YH) of a most bulged position H in a heel side of the head body and a Y coordinate value (YB) of a most bulged position B in a backside of the head body are respectively set equal to 2 mm or lower.
According to the foregoing golf club head, preferably, an absolute value of a sum of an X coordinate value (XT) of the most bulged position T in the toe side of the head body and an X coordinate value (XH) of the most bulged position H in the heel side of the head body is set equal to 2 mm or lower, an absolute value of a difference between a Z coordinate value (ZT) of the most bulged position T in the toe side of the head body and a Z coordinate value (ZH) of the most bulged position H in the heel side of the head body is set equal to 2 mm or lower, and absolute values of an X coordinate value (XC) of the most bulged position C in the crown side of the head body, an X coordinate value (XS) of the most bulged position S in the sole side of the head body and an X coordinate value (XB) of the most bulged position B in the backside of the head body are respectively set equal to 2 mm or lower.
Thus, in a three-dimensional coordinate axis with the face center set as the origin, by defining the coordinate value of each most bulged position in the head body within the foregoing range and bringing a shape of the head body close to that of symmetry in an upper-lower direction, more preferably to that of symmetry in upper-lower and right-left directions, a position of a head center of gravity projected on the face surface can be set in the vicinity of the face center without disposing any weights in the sole side or increasing a thickness of the sole portion. If there is room for further addition of a weight, it is possible to set the head center of gravity much lower and deeper. Moreover, even when a head thickness is reduced within a range permitted by a strength, and a head volume is increased to a maximum, the head center of gravity projected on the face surface can be set in the vicinity of the face center.
According to the present invention, the geometrical face center of the face surface is a centroid of the face surface. In addition, the X axis as the straight line extended in the right-left toe-heel direction is an axis parallel to an installation surface (ground surface) when the golf club head is installed according to a lie angle.
In this case, the installation according to the lie angle means a state where spaces between a round of the sole surface of the head and the installation surface as a plane surface are roughly equal to each other in the toe and heel sides. If the round of the sole surface is ambiguous, a score line and the installation surface are set parallel to each other. If the parallel state with the installation surface cannot be determined, e.g., the round of the sole surface is ambiguous, or the score line is not straight, a lie angle (degree)=(100xe2x88x92club length (inch)) is set. For example, when a club length is 44 inches, a lie angle is 100xe2x88x9244=56xc2x0.
A club length is measured by a traditional standard measuring method set as a standard by The Japan Golf Goods Association. That is, a length is set from a contact between a sole surface of a head and a back of a neck portion to a grip end (not including a round cap portion). For a measuring device, a Club Measure II by Kamoshita Seikoujo Co., Ltd. may be used.